The annual market for air freshener products in the U.S. is over $3 billion. Plug-in type air freshener products account for a third of that market. Over the past decade, battery-operated, metered aerosol fragrance dispensers have become popular in commercial settings such as public and office restrooms. As these devices are typically somewhat complex, in that they incorporate a DC electric motor, a gear drive operated by the motor which actuates the spray valve, an aerosol fragrance canister, and a programmable timer for adjusting the time interval between sprays, average retail prices of around $50 were too costly to generate widespread demand for home use. However, prices have dropped dramatically. For example, Wal-Mart now sells a programmable Air Wick® dispenser with one aerosol fragrance canister for less than $10. As the cost of a replacement fragrance canister is nearly $4, it appears that American Home Products Corporation may be selling the Air Wick® fragrance dispenser at less than cost, a marketing strategy learned from Gillette's sale of razor blades and Hewlett-Packard's sale of ink cartridges.
One problem associated with the motor-operated fragrance dispensers is that the moving mechanical parts are the components most likely to fail over time. A simpler, more durable solution employs a micro-perforated plate secured to a piezoelectric vibrator that is energized by an AC voltage. Such devices have been used as humidifiers and as aerosol fragrance dispensers. U.S. Pat. No. 5,297,734 to Kohji Toda discloses such an ultrasonic vibrating device. The micro-perforations are conical and larger in diameter on the supply side, and the piezoelectric vibrator operates at a frequency of about 100 kHz.
U.S. Pat. No. 5,657,926, also to Kohji Toda, discloses an ultrasonic atomizing device that employs electrical feedback from the piezoelectric vibrator to generate a resonant frequency of greater amplitude to vibrate the micro-perforated plate.
U.S. Pat. No. 6,293,474 to Thomas A. Helf, et al. discloses a wick-based delivery system to provide liquid to a micro-perforated plate that is vibrated by a piezoelectric device.
U.S. Pat. No. 6,341,732 to Frederick H. Martin, et al. discloses a method and apparatus for maintaining control of liquid flow in a vibratory atomizing device. As with the '474 Patent to Helf, et al., liquid if provided to a vibrating orifice plate by a wick. However, liquid that is not expelled by the vibrating plate drains back through the plate and absorbed by the wick, which then provides it again to the vibrating plate.